The present invention relates to blood roller pumps, and particularly to the blood tubing used with such roller pumps.
Roller pumps are specifically used to pump blood through an extracorporeal circuit. These types of pumps are formed with a generally circular raceway into which a blood compatible tubing is fixed. The tubing includes inlet and outlet ends. The pumps also include one or more rollers. These rollers are rotatably mounted to the ends of individual arms, which rotate about a common axis to direct the rollers along the pump raceway. The pumping action is obtained by the compressing of the tubing as the rollers are pushed along the raceway. An example of a roller pump is the Sarns 7000.
The pumping rate achieved by roller pumps is dependent upon the size of the tubing held within the raceway, and/or the rate of compression applied by the pressure rollers. Faster rotation rates increase the rate of compression of the tubing. This increased compression can lead to greater hemolysis. It is thus more desireable to increase the pump rate by increasing the diameter of the tubing in the pump raceway. A limitation on the diameter of the raceway tubing is the diameter of the tubing in the remainder of the circuit, which is constrained by the size of the other elements positioned in the raceway.
One alternative suggested by various workers is the positioning of a larger diameter tube or bulb in the pump raceway which is coupled to the smaller diameter tubing comprising the circuit by suitable connectors. Examples of such arrangements are disclosed in U.S. Pat. Nos. 3,046,903, issued to Jones on July 31, 1962; and 4,347,874, issued to Sullivan et al on Sept. 7, 1982.
The disadvantage with such arrangements is the sharp surfaces provided by the connectors. Hemolysis occurs as the blood passes through such connectors. It would be highly desirable to provide for a continuous length of tubing having a larger internal diameter for placement in the pump raceway.
Single tubes having section of differing diameters haven been used in other types of fluid pumps, and specifically in peristaltic pumps. For example, see U.S. patent application Ser. No. 830,693, filed on Feb. 18, 1986, entitled COLLAPSIBLE CONDUIT FOR LINEAR PERISTALTIC PUMP AND METHOD OF MAKING SAME, which is assigned to the same assignee of the instant application. The major disadvantage to the disclosed tube is the required thin wall portion which is placed in the pump.
Peristaltic pumps include a tube positioned in a chamber partially defined by a series of reciprocating cams. The operation of the peristaltic pump involves the sequential receiprocation of the cams to laterally compress the tube. As stated, roller pumps operate by compressing a tube positioned in the pump raceway by the action of revolving rollers. The tube is slightly stretched as the rollers are passed along the tube. It has been discovered that this slight stretching action damages the thin walled portion of the tube described in the previously mentioned application.
The formation of a unitary tube having more than one diameter is disclosed in U.S. Pat. No. 4,499,045, issued to Obsomer on Feb. 12, 1985. This patent discloses a process whereby a tube is heated and then compressed inwardly into a chamber. The inward compression allows the tube to laterally expand while maintaining the molecular orientation of the plastic forming the tube. The overall length of the tube is constrained by the size of the mold into which the tube is compressed. Furthermore, the resulting tube possesses sharp surfaces which presents the same problems associated with the interconnecting of two different diametered tubes.